U.S. patent application number 15/070695 was filed with the patent office on 2016-09-22 for motor drive controller and method for controlling motor.
The applicant listed for this patent is MINEBEA CO., LTD.. Invention is credited to Takayuki MATSUI, Shigeki MIYAJI, Tetsuya SEKI.
Application Number | 20160276974 15/070695 |
Document ID | / |
Family ID | 56853220 |
Filed Date | 2016-09-22 |
United States Patent
Application |
20160276974 |
Kind Code |
A1 |
MIYAJI; Shigeki ; et
al. |
September 22, 2016 |
MOTOR DRIVE CONTROLLER AND METHOD FOR CONTROLLING MOTOR
Abstract
A motor drive controller includes: a control circuit that
controls an AC current flowing in a motor; a frequency modulation
unit that frequency-modulates a speed of the motor when the motor
is driven at a predetermined speed; and a current effective value
controller that decreases an effective value of the AC current
flowing in the motor as the speed of the motor modulated by the
frequency modulation unit becomes closer to a resonant frequency of
the motor.
Inventors: |
MIYAJI; Shigeki;
(HAMAMATSU-CITY, JP) ; MATSUI; Takayuki;
(TOYOHASHI-CITY, JP) ; SEKI; Tetsuya;
(FUKUROI-CITY, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MINEBEA CO., LTD. |
KITASAKU-GUN |
|
JP |
|
|
Family ID: |
56853220 |
Appl. No.: |
15/070695 |
Filed: |
March 15, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02P 29/50 20160201;
H02P 8/32 20130101 |
International
Class: |
H02P 27/06 20060101
H02P027/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2015 |
JP |
2015-053468 |
Claims
1. A motor drive controller comprising: a control circuit that
controls an AC current flowing in a motor; a frequency modulation
unit that frequency-modulates a speed of the motor when the motor
is driven at a predetermined speed; and a current effective value
controller that decreases an effective value of the AC current
flowing in the motor as the speed of the motor modulated by the
frequency modulation unit becomes closer to a resonant frequency of
the motor.
2. The motor drive controller according to claim 1, wherein when a
predetermined speed at which the motor is driven is higher than the
resonant frequency of the motor, the current effective value
controller decreases the effective value of the AC current flowing
in the motor to suppress a variation in vibration of the motor as
the speed of the motor decreases.
3. The motor drive controller according to claim 2, wherein the
frequency modulation unit includes a table of frequencies, and
wherein the current effective value controller includes a table of
current gains that vary with the same phase as that of the
frequency modulation unit.
4. The motor drive controller according to claim 1, wherein when
the predetermined speed at which the motor is driven is lower than
the resonant frequency of the motor, the current effective value
controller increases the effective value of the AC current flowing
in the motor to suppress a variation in vibration of the motor as
the speed of the motor decreases.
5. A motor drive controller comprising: a control circuit that
controls an AC current flowing in a motor; a frequency modulation
unit that frequency-modulates a speed of the motor when the motor
is driven at a predetermined speed; and a current effective value
controller that frequency-modulates an effective value of the AC
current flowing in the motor with the same phase as a variation of
the speed of the motor by the frequency modulation unit.
6. A method for controlling a motor, the method comprising:
controlling an AC current supplied to the motor to
frequency-modulate a speed of the motor when the motor is driven at
a predetermined speed; and decreasing an effective value of the AC
current flowing in the motor as the speed of the motor modulated by
the frequency-modulation becomes closer to a resonant frequency of
the motor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a motor drive controller
and a method for controlling a motor.
[0003] 2. Description of the Related Art
[0004] In paragraph 0030 of JP-A-H06(1994)-245590, it is described
that "noise generated from a pulse motor can be greatly reduced by
periodically modulating a motor driving frequency in a constant
speed rotation period."
[0005] In paragraph 0006 of JP-A-H06(1994)-245590, it is described
that "when a pulse motor is driven at a steady speed (fo), the
pulse motor is driven by superimposing a signal with a modulation
width (.DELTA.f) varying in a period (1/fs) at the steady speed
(fo)." In paragraphs 0022 to 0027 of JP-A-H06(1994)-245590, it is
described that "setting ranges of the period (1/fs) and the
modulation width (.DELTA.f) in which a good noise reduction effect
is obtained."
[0006] When a stepping motor has a resonant frequency at a
predetermined drive speed and the motor is driven at a speed close
to the resonant frequency, there were problems that large vibration
ripples occur based on a frequency modulation and abnormal noise
(beat noise) occurs. There is also a problem that torque ripples
occur due to the frequency modulation.
SUMMARY OF THE INVENTION
[0007] One of objects of the present invention is to provide a
motor drive controller and a method for controlling a motor that
can suppress abnormal noises or torque ripples generated in
periodically modulating a driving frequency of the stepping
motor.
[0008] According to an illustrative embodiment of the present
invention, there is provided a motor drive controller including: a
control circuit that controls an AC current flowing in a motor; a
frequency modulation unit that frequency-modulates a speed of the
motor when the motor is driven at a predetermined speed; and a
current effective value controller that decreases an effective
value of the AC current flowing in the motor as the speed of the
motor modulated by the frequency modulation unit becomes closer to
a resonant frequency of the motor.
[0009] According to another illustrative embodiment of the present
invention, there is provided a motor drive controller including: a
control circuit that controls an AC current flowing in a motor; a
frequency modulation unit that frequency-modulates a speed of the
motor when the motor is driven at a predetermined speed; and a
current effective value controller that frequency-modulates an
effective value of the AC current flowing in the motor with the
same phase as a variation of the speed of the motor by the
frequency modulation unit.
[0010] According to still another illustrative embodiment of the
present invention, there is provided a method for controlling a
motor, the method including: controlling an AC current supplied to
the motor to frequency-modulate a speed of the motor when the motor
is driven at a predetermined speed; and decreasing an effective
value of the AC current flowing in the motor as the speed of the
motor modulated by the frequency-modulation becomes closer to a
resonant frequency of the motor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] In the accompanying drawings:
[0012] FIG. 1 is a diagram schematically illustrating a
configuration of a motor drive controller according to an
embodiment of the present invention;
[0013] FIG. 2 is a detailed block diagram of the motor drive
controller according to the embodiment of the present
invention;
[0014] FIG. 3 is a diagram illustrating an operation of suppressing
an abnormal noise when frequency modulation is performed at a
higher speed range than a resonant frequency;
[0015] FIG. 4 is a diagram illustrating an operation of suppressing
an abnormal noise when frequency modulation is performed at a lower
speed range than a resonant frequency;
[0016] FIG. 5 is a diagram illustrating an operation of suppressing
a torque variation;
[0017] FIG. 6 is a waveform diagram illustrating a relationship
between a frequency modulation and a reference current value,
[0018] FIG. 7 is a diagram illustrating an example of the reference
current value in which one period is divided into 32 sections;
[0019] FIGS. 8A and 8B are flowcharts illustrating a control
process and a setting process of the reference current value
according to the embodiment; and
[0020] FIGS. 9A and 9B are diagrams illustrating causes of
vibration and abnormal noise according to a comparative
example.
DETAILED DESCRIPTION
[0021] Hereinafter, embodiment of the present invention will be
described in detail with reference to the accompanying
drawings.
[0022] FIG. 1 is a diagram schematically illustrating a
configuration of a motor drive controller 100 according to an
embodiment of the present invention.
[0023] In FIG. 1, a stepping motor 120 is a bipolar-type two-phase
stepping motor, and includes a rotor 126 that has a permanent
magnet and is rotatably provided and stators 122XP, 122XN, 122YP,
and 122YN that are formed at four equal positions in the
circumferential direction of the periphery of the rotor 126. The
stators 122 XP and 122XN configure an X phase. The stators 122YP
and 122YN configure a Y phase. Hereinafter, when each stator is not
particularly distinguished from each other, there is a case of
simply describing the stator 122
[0024] A winding wire is wound around each of the stators. Winding
wires wound around the stators 122YP and 122YN are connected to
each other in series and the winding wires are denoted together by
"a stator winding wire 124Y." In the same way, winding wires wound
around the stators 122XP and 122XN are connected to each other in
series and the winding wires are denoted together by "a stator
winding wire 124X."
[0025] A host device 130 outputs a speed command signal of
commanding a rotation speed of the stepping motor 120. A motor
drive controller 100 drives and controls the stepping motor 120 in
response to the speed command signal. The motor drive controller
100 includes H bridge circuits 20X and 20Y that apply an X-phase
voltage VMX and a Y-phase voltage VMY to the stator winding wires
124X and 124Y, respectively.
[0026] FIG. 2 is a detailed block diagram of a motor drive
controller 100. FIG. 1 illustrates two sets of stator winding wires
124X and 124Y and two sets of H bridge circuits 20X and 20Y, but
FIG. 2 illustrates one of the stator winding wires as a stator
winding wire 124 and illustrates one of the H bridge circuits as an
H bridge circuit 20.
[0027] A processor (central processing unit (CPU)) 101 mounted in
the motor drive controller 100 controls each unit based on various
tables or control programs stored in a read only memory (ROM) 103.
A timer 102 measures time elapsed from the reset timing under
control of the CPU 101. A bridge controller 108 controls each unit
of a bridge control circuit 110 (control circuit) based on a
command from the CPU 101, and thus controls AC current flowing in
the stepping motor 120. A multiplier 107 is controlled by the CPU
101 and multiples a parameter by a gain, and outputs the result of
the operation.
[0028] A comparison current table 104, a current gain table 105,
and a frequency modulation table 106 are stored in the ROM 103 in
the motor drive controller 100 according to the embodiment of the
present invention.
[0029] In the comparison current table 104, a sequence of
comparison current values in a micro step is stored. The micro step
means a unit of control for accurately controlling the stepping
motor 120 than a control based on a basic step angle of 90 degrees
of the stepping motor 120. Compared with a case in which a motor is
driven in a full step, it is possible to effectively reduce
vibration or noise generated at a low speed by driving the stepping
motor 120 in the micro step. Here, the comparison current values of
the comparison current table 104 are stored and configured to form
a sinusoidal wave as a whole.
[0030] In the current gain table 105, a sequence of a current gain
value when a reference current value Iref is calculated by
multiplying the comparison current is stored. The current gain
changes an effective value of an AC current flowing in the motor
and the sequence of the current gain value becomes a value varying
in a sinusoidal wave synchronized to a frequency modulation which
will be described later. An effective value of the AC current
flowing in the motor can be controlled by the current gain table
105, which serves to operate the CPU 101 as a current effective
value controller.
[0031] In the frequency modulation table 106, a sequence of a
period of the micro step is stored. Here, the sequence of the
period of the micro step becomes a value varying in a sinusoidal
wave because the motor drive controller 100 performs a frequency
modulation on a speed of the motor. When the stepping motor 120 is
driven at a predetermined rotation speed by the frequency
modulation table 106, which serves to operate the CPU 101 as a
frequency modulation unit, a frequency modulation is performed on
the rotation speed. As a result, a noise of the stepping motor 120
can be greatly reduced.
[0032] Hereinafter, the frequency modulation of the motor drive
controller 100 in a comparative example and the embodiment will be
described. In the comparative example, while performing the
frequency modulation based on the frequency modulation table 106, a
comparison current of a micro step is outputted as a reference
current value Iref. An example of a waveform at this time is
illustrated in FIGS. 9A and 9B which will be described later.
[0033] On the contrary, the motor drive controller 100 of the
embodiment multiplies a comparison current of the micro step by a
current gain synchronized to the frequency modulation while
performing the frequency modulation based on the frequency
modulation table 106 and outputs the multiplied current as a
reference current value Iref.
[0034] The bridge control circuit 110 is configured as a single
integrated circuit. In the bridge control circuit 110, a pulse
width modulation (PWM) signal generator 111 generates a PWM signal
and supplies the PWM signal to the H bridge circuit 20 based on a
control of the bridge controller 108. A field effect transistor FET
is bridged to the H bridge circuit 20, and the PWM signal supplied
to the H bridge circuit 20 is an ON/OFF signal applied to the FET
as a gate voltage.
[0035] Based on the PWM signal, the H bridge circuit 20 generates a
motor voltage and applies the generated motor voltage to the stator
winding wire 124 of the stepping motor 120. The motor voltage is
actually an X-phase voltage VMX and a Y-phase voltage VMY
illustrated in FIG. 1.
[0036] A current detector 113 outputs a current measurement value
Icoil of a current flowing in the stator winding wire 124 by
measuring a value of a current flowing in the H bridge circuit 20
in a current direction. A D/A converter 112 receives the reference
current value Iref as a digital value from the bridge controller
108 and converts the digital value into an analog value. A
comparator 114 compares the current measurement value Icoil as the
analog value with the reference current value Iref. The comparator
outputs a signal "1" when the former is equal to or greater than
the latter, but outputs a signal "0" when the former is smaller
than the latter. The comparison signal is input to the bridge
controller 108. The bridge controller 108 can control the current
measurement value Icoil to be closer to the reference current value
Iref based on the comparison signal.
[0037] FIGS. 9A and 9B are diagrams illustrating a cause of
vibration and abnormal noise in the comparative example.
[0038] FIG. 9A is a diagram illustrating a frequency modulation in
the comparative example. A vertical axis in FIG. 9A indicates the
vibration of the stepping motor 120 and a horizontal axis indicates
a speed of the stepping motor 120. The vibration has a peak value
due to resonance at the resonant frequency fr of the stepping motor
120. A frequency modulation graph of the speed of the stepping
motor 120 is superimposed on a graph illustrated in FIG. 9A. In the
graph, a downward direction indicates a time elapse and a lateral
direction indicates a speed.
[0039] In the comparative example of FIG. 9A, the stepping motor
120 is rotated and frequency modulation is performed at a higher
speed than the resonant frequency fr of the stepping motor 120
(referring to FIG. 2). At this time, when the speed of the stepping
motor 120 increases, the vibration due to resonance decreases, and
when the speed decreases, the vibration due to resonance increases.
As a frequency of the frequency modulation belongs in an audible
region, the variation in vibration is sounded as abnormal noise
(beat sound).
[0040] FIG. 9B is a waveform chart illustrating frequency
modulation of the comparative example. A vertical axis of FIG. 9B
indicates the vibration of the stepping motor 120, and a horizontal
axis indicates a time.
[0041] FIG. 9B illustrates that when the speed of the stepping
motor 120 increases, the vibration due to resonance decreases and
when the speed of the stepping motor 120 decreases, the vibration
due to resonance increases.
[0042] An operation of the embodiment will be described with
reference to FIGS. 3 to 8B. The motor drive controller 100 of the
embodiment controls a current flowing in the stepping motor 120 in
response to a rotation speed of the stepping motor 120 by the
frequency modulation. As a result, it is possible to suppress
abnormal noise or/and torque ripples.
[0043] FIG. 3 is a diagram illustrating an operation of suppressing
abnormal noise when frequency modulation is applied in a higher
range than the resonant frequency fr.
[0044] Section (a) of FIG. 3 is a diagram illustrating frequency
modulation. A vertical axis of section (a) of FIG. 3 indicates
vibration of the stepping motor 120 and a horizontal axis indicates
a speed of the stepping motor 120. The vibration has a peak value
due to resonance at the resonant frequency fr of the stepping motor
120. A frequency modulation graph of the speed of the stepping
motor 120 is superimposed on a graph illustrated in section (a) of
FIG. 3. In the graph, a downward direction indicates a time elapse
and a lateral direction indicates a speed.
[0045] Section (b) of FIG. 3 is a graph illustrating temporal
variation of the speed with the frequency modulation. The speed of
the stepping motor 120 varies in the form of a sine wave around a
predetermined speed. All of origin vertical axis of sections
(b)-(e) of FIG. 3 indicate a center value of the frequency
modulation.
[0046] Section (c) of FIG. 3 is a graph illustrating a temporal
variation in vibration as a whole by the frequency modulation when
a motor current is set to be constant. By resonance, vibration of
the stepping motor 120 varies with respect to a predetermined value
in the form of a sine wave and with a reverse phase against the
speed.
[0047] Section (d) of FIG. 3 is a graph illustrating temporal
variation of an effective value of a motor current by the control
according to the embodiment. In the embodiment, the effective value
of the motor current of the stepping motor 120 is varied in the
form of the sine wave and with the same phase as the speed. Here,
the effective value of the motor current is controlled by the
reference current value Iref. The effective value of the motor
current can be controlled to vary in the form of the sine wave and
with the same phase as the speed by varying a current gain for
calculating the reference current value Iref in the form of the
sine wave and with the same phase as the frequency modulation
around a predetermined value (for example, 1.0).
[0048] Torque varies in proportion to the effective value of the
motor current and vibration due to the torque varies. Therefore, by
controlling the effective value of the motor current in the form of
a sine wave and with the same phase as the speed, the vibration due
to the torque can vary in the form of a sine wave and with the same
phase as the speed and a variation of resonant vibration by the
frequency modulation can be removed.
[0049] That is, as the speed of the stepping motor 120 by the
frequency modulation becomes closer to the resonant frequency of
the stepping motor 120, the current gain of the current gain table
105 is controlled to decrease so as to make an AC current flowing
in the stepping motor 120 have a small effective value.
[0050] Since a predetermined speed at which the stepping motor 120
is driven is higher than the resonant frequency of the stepping
motor 120, the current gain table 105 is configured such that the
current gain increases as the speed of the stepping motor 120
increases. That is, the current gain table 105 is configured to
include a table of current gain varying with the same phase as the
frequency modulation.
[0051] Section (e) of FIG. 3 is a graph illustrating a suppression
result of the variation in vibration as a whole by the control of
the embodiment. A dashed line represents the variation in vibration
when the motor current is set to be constant in section (c) of FIG.
3, and a solid line represents that variation in vibration as a
whole is suppressed by the control according to the embodiment.
According to the embodiment, it is possible to remove the temporal
variation in resonant vibration by the frequency modulation using
the variation in vibration due to the torque and thus to suppress
abnormal noise.
[0052] FIG. 4 is a diagram illustrating an operation of suppressing
abnormal noise when the frequency modulation is performed in a
lower range than the resonant frequency fr.
[0053] Section (a) of FIG. 4 is a diagram illustrating frequency
modulation. A vertical axis of FIG. 4A indicates vibration of the
stepping motor 120 and a horizontal axis indicates a speed of the
stepping motor 120. The vibration has a peak value due to resonance
at the resonant frequency fr of the stepping motor 120. A frequency
modulation graph of the speed of the stepping motor 120 is
superimposed on the graph illustrated in FIG. 4A. In the graph, a
downward direction indicates a time elapse and a lateral direction
indicates a speed.
[0054] Section (b) of FIG. 4 is a graph illustrating temporal
variation of the speed with the frequency modulation. The speed of
the stepping motor 120 varies in the form of a sine wave around a
predetermined speed. All of origin vertical axis of sections
(b)-(e) of FIG. 4 indicate a center value of the frequency
modulation.
[0055] Section (c) of FIG. 4 is a graph illustrating a temporal
variation in vibration by the frequency modulation when a motor
current is set to be constant. By resonance, the vibration of the
stepping motor 120 varies with respect to a predetermined value in
the form of a sine wave and with the same phase as the speed.
[0056] Section (d) of FIG. 4 is a graph illustrating temporal
variation of an effective value of a motor current by the control
according to the embodiment. In the embodiment, the effective value
of the motor current of the stepping motor 120 is varied in the
form of the sine wave and with the reverse phase against the speed.
Here, the effective value of the motor current is controlled by the
reference current value Iref. The effective value of the motor
current can be controlled to vary in the form of the sine wave and
with the reverse phase against the speed by varying a current gain
for calculating the reference current value Iref in the form of the
sine wave and with the reverse phase against the frequency
modulation around a predetermined value (for example, 1.0).
[0057] Torque varies in proportion to the effective value of the
motor current and vibration due to the torque varies. Therefore, by
controlling the effective value of the motor current in the form of
a sine wave and with the reverse phase against the speed, the
vibration due to the torque can vary in the form of a sine wave and
with the reverse phase against the speed and the variation of
resonant vibration by the frequency modulation can be removed.
[0058] That is, as the speed of the stepping motor 120 by the
frequency modulation becomes closer to the resonant frequency of
the stepping motor 120, the current gain of the current gain table
105 is controlled to decrease so as to make an AC current flowing
in the stepping motor 120 have a small effective value.
[0059] At this time, since a predetermined speed at which the
stepping motor 120 is driven is lower than the resonant frequency
of the stepping motor 120, the current gain table 105 is configured
such that the current gain decreases as the speed of the stepping
motor 120 increases. That is, the current gain table 105 is
configured to include a table of current gains varying with the
reverse phase against the frequency modulation.
[0060] Section (e) of FIG. 4 is a graph illustrating a suppression
result of a variation of total vibration by the control according
to the embodiment. A dashed line represents variation of vibrations
when the motor current is set to be constant in section (c) of FIG.
4, and a solid line represents that variation of the overall
vibrations is suppressed by the control of the embodiment.
According to the embodiment, it is possible to remove the temporal
variation of the resonant vibration by the frequency modulation
using the variation in vibration due to the torque and thus to
suppress abnormal noise.
[0061] FIG. 5 is a diagram illustrating an operation of suppressing
torque variation with frequency modulation.
[0062] Section (a) of FIG. 5 is a graph illustrating a temporal
variation of the speed by the frequency modulation. The speed of
the stepping motor 120 varies in the form of a sine wave around a
predetermined speed. All of origin vertical axis of sections
(a)-(d) of FIG. 5 indicate a center value of the frequency
modulation.
[0063] Section (b) of FIG. 5 is a graph illustrating temporal
variation of torque with the frequency modulation when a motor
current is set to be constant. As the speed of the stepping motor
120 increases, the torque decreases. But, as the speed of the
stepping motor 120 decreases, the torque increases. That is, the
torque of the stepping motor 120 varies with respect to a
predetermined value in the form of a sine wave and with the reverse
phase against the speed.
[0064] Section (c) of FIG. 5 is a graph illustrating a temporal
variation of an effective value of a motor current by the control
according to the embodiment. In the embodiment, the effective value
of the motor current of the stepping motor 120 is varied in the
form of the sine wave and with the same phase as the speed. Here,
the effective value of the motor current can be controlled to vary
in the form of the sine wave and with the same phase as the speed
by varying a current gain for calculating the reference current
value Iref in the form of the sine wave and with the same phase as
the frequency modulation around a predetermined value (for example,
1.0).
[0065] Torque varies in proportion to the effective value of the
motor current. Therefore, by controlling the effective value of the
motor current in the form of a sine wave and with the same phase as
the speed, the torque can vary in the form of a sine wave and with
the reverse phase against the speed and a variation in torque by
the frequency modulation can be removed.
[0066] That is, the current gain table 105 includes a table of
current gains varying with the same phase as the speed of the
stepping motor 120 by the frequency modulation. As a result, the
effective value of the motor current can be controlled to vary in
the form of a sine wave and with the same phase as the speed.
[0067] Section (d) of FIG. 5 is a graph illustrating a suppression
result of a variation in vibration as a whole by the control
according to the embodiment. A dashed line represents the variation
in vibration when the motor current is set to be constant in
section (b) of FIG. 5, and a solid line represents that the
variation in vibration as a whole is suppressed by the control of
the embodiment. According to the embodiment, it is possible to
remove variation of the torque with the frequency modulation by
using variation of the torque based on the effective value of the
motor current and thus to suppress torque ripples.
[0068] FIG. 6 is a waveform chart illustrating relationship between
the frequency modulation and a reference current value Iref. At
this time, the speed of the stepping motor 120 is higher than the
resonant frequency fr.
[0069] A vertical axis of section (a) of FIG. 6 indicates a speed,
and a horizontal axis indicates common time. The speed of the
stepping motor 120 varies in the form of a sine wave around a
predetermined value.
[0070] A vertical axis of section (b) of FIG. 6 indicates a
reference current value Iref, and a horizontal axis indicates
common time. An envelope of the reference current value Iref of the
stepping motor 120 varies in the form of a sine wave and with the
same phase as the speed. Here, the envelope of the reference
current value Iref indicates an effective value of a motor
current.
[0071] When an amplitude of the envelope of the reference current
value Iref is small, the reference current value Iref decreases,
but when the amplitude of the envelope of the reference current
value Iref is great, the reference current value Iref increases. A
variation in vibration can be suppressed using the control
method.
[0072] FIG. 7 is a diagram illustrating an example of the reference
current value Iref of each micro step in which 1 period is divided
into 32 sections. A vertical axis of FIG. 7 indicates a reference
current value Iref, and a horizontal axis indicates time. 1 period
is divided into 32 micro steps. The reference current value Iref
has a sinusoidal form.
[0073] Every period Tm of micro steps becomes current setting
timing illustrated in thin arrows. Every period becomes frequency
modulation timing illustrated in thick arrows.
[0074] FIGS. 8A and 8B are flowcharts illustrating a control
process and a process of setting the reference current value Iref
according to this embodiment.
[0075] FIG. 8A indicates a control process of the reference current
value Iref in a main routine.
[0076] The main routine starts when the motor drive controller 100
is activated.
[0077] The CPU 101 of the motor drive controller 100 performs
initial setting of the units in step S10, and allows an
interruption of the timer 102 in step S11. In the timer 102, an
initial micro step period of the frequency modulation table 106 is
set. As a result, the timer interruption illustrated in FIG. 8B is
activated.
[0078] Then, the CPU 101 repeats the current control of controlling
the reference current value Iref to be a target value in the bridge
controller 108. The reference current value Iref is set by the
timer interruption.
[0079] FIG. 8B illustrates a process of setting the reference
current value Iref by the timer interruption. The reference current
value Iref is set by the timer interruption and thus a micro step
starts.
[0080] When the timer interruption is activated, the CPU 101
determines whether it is a frequency modulation timing or not in
step S20. As illustrated in FIG. 7, the frequency modulation timing
in this embodiment arrives once a period and once per 32 micro
steps. When it is determined that it is a frequency modulation
timing (YES in step S20), the CPU 101 performs the processes of
steps S21 and S22 relevant to the frequency modulation timing.
[0081] In step S21 relevant to the frequency modulation timing, the
CPU 101 causes the timer 102 to set a period of the next micro step
from the frequency modulation table 106, sets a current gain of the
present micro step from the current gain table 105 (step S22), and
then performs the processes of steps S23 and S24 relevant to the
current setting timing.
[0082] In step S20, when it is determined that it is not a
frequency modulation timing (NO in step S20), the CPU 101 performs
the processes of steps S23 and S24 relevant to the current setting
timing.
[0083] In step S23 relevant to the current setting timing, the CPU
101 sets a comparison current value of the present micro step of
the comparison current table 104, multiplies the comparison current
value by a current gain to calculate the reference current value
Iref (step S24), and returns to the original process.
[0084] In the embodiment, when the motor is rotated by a faster
speed than the resonant frequency fr of the motor, the motor
current is controlled to be greater than the comparison current
value as the rotation speed is increased by the frequency
modulation. The motor current is controlled to be smaller than the
comparison current value as the rotation speed is decreased.
[0085] When the motor is rotated by a slower speed than the
resonant frequency fr of the motor, the motor current is controlled
to be smaller than the comparison current value as the rotation
speed is increased by the frequency modulation. The motor current
is controlled to be greater than the comparison current value as
the rotation speed is decreased.
[0086] That is, the motor current is controlled to be smaller than
the comparison current value in response to the rotation speed as
the rotation speed becomes closer to the resonant frequency fr by
the frequency modulation, and the motor current is controlled to be
greater than the comparison current value in response to the
rotation speed as the rotation speed gets separated away from the
resonant frequency fr. As a result, vibration ripples can be
suppressed and thus the abnormal noise (beat sound) can be reduced.
Because the vibration ripples of the motor can be suppressed, it is
possible to suppress vibration and noise of an actuator in which
the motor is mounted.
[0087] The motor current is controlled to be greater than the
comparison current value in response to the rotation speed as the
rotation speed is increased by the frequency modulation, and the
motor current is controlled to be smaller than the comparison
current value in response to the rotation speed as the rotation
speed is decreased.
[0088] Through this control, the torque ripples can be reduced.
Since the torque ripples can be suppressed, it is possible to
stably rotate a load attached to the motor.
[0089] The present invention is not limited to the above-mentioned
embodiment and can be modified in various forms without departing
from the gist of the present invention. For example, Modified
Examples (a) to (e) described below can be considered.
[0090] (a) In the embodiment, current setting of the motor is
performed in the same timing as setting of the frequency modulation
of the speed of the motor, but may be performed in a separate
timing.
[0091] (b) The processes of steps S21 and S22 performed in the
frequency modulation timing may be performed every predetermined
period without limiting to 1 period. For example, processes of the
steps S21 and S22 may be performed every two period. The current
setting timing is not limited to 32 times a period. The times can
be arbitrarily set.
[0092] (c) In the embodiment, while being controlled by the
frequency modulation table 106 and the current gain table 105,
numerical values of the frequency modulation or the current gain
may be derived by a calculation.
[0093] (d) In the embodiment, different operations are performed
depending on whether the speed is higher than the resonant
frequency fr of the stepping motor 120 or not. However, the present
invention is not limited thereto and it may be determined whether
the speed is higher than the resonant frequency fr of the stepping
motor 120 or not and a corresponding current gain table 105 may be
selected and used.
[0094] (e) In the embodiment, while the frequency modulation having
a sinusoidal waveform is applied to the motor speed and a current
setting having the sinusoidal waveform synchronized thereto is
performed, the current setting may have any of the vibration
waveform and is not limited to the sinusoidal waveform as long as
the motor speed is synchronized to the motor current.
[0095] As described in the above with reference to the embodiment
and modified examples, according to the present invention, it is
possible to suppress abnormal noises or torque ripples generated in
periodically modulating a driving frequency of the stepping
motor.
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